Fibronectin-Induced Proliferation in Thyroid Cells. Xanya Sofra Weiss

Maddalena Illario, Anna Lina Cavallo, Sara Monaco, Ennio Di Vito, Frank Mueller, Luigi A. Marzano, Giancarlo Troncone, Gianfranco Fenzi, Guido Rossi, and Mario Vitale

Werecently demonstrated in an immortalized thyroid cell line that integrin stimulation by fibronectin (FN) simultaneously activates two signaling pathways: Ras/Raf/MAPK kinase (Mek)/Erk and calcium (Ca2 )/calcium calmodulin-dependent kinase II (CaMKII). Both signals are necessary to stimulate Erk phosphorylation because CaMKII modulates Ras-induced Raf-1 activity. In this study we present evidence that extends these findings to normal human thyroid cells in primary culture, demonstrating its biological significance in a more physiological cell model. In normal thyroid cells, immobilized FNinduced activation of p21Ras and Erk phosphorylation. This pathway was responsible for FN-induced cell proliferation. Concurrent increase of intracellular Ca2 concentration and CaMKII activation was observed. Both induction of p21Ras activity and increase of intracellular Ca2 concentration were
mediated by FN binding to v 3 integrin. Inhibition of the Ca2 /CaMKII signal pathway by calmodulin or CaMKII inhibitors completely abolished the FN-induced Erk phosphorylation. Binding to FN induced Raf-1 and CaMKII to form a protein complex, indicating that intersection between Ras/Raf/ Mek/Erk and Ca2 /CaMKII signaling pathways occurred at Raf-1 level. Interruption of the Ca2 /CaMKII signal pathway arrested cell proliferation induced by FN. We also analyzed thyroid tumor cell lines that displayed concomitant aberrant integrin expression and signal transduction. These data confirm that integrin activation by FN in normal thyroid cells generates Ras/Raf/Mek/Erk and Ca2 /CaMKII signaling pathways and that both are necessary to stimulate cell proliferation, whereas in thyroid tumors integrin signaling is altered. (J Clin Endocrinol Metab 90: 2865–2873, 2005)

Xanya Sofra Weiss

Xanya Sofra Weiss